A second fiber expert brought in by the Wayne B. Williams defense team today examined evidence that prosecutors contend links Williams with 12 murdered black youths.

A court order allowed Randall R. Bresee, an assistant professor at Kansas State University, to visit the Georgia state crime lab today and examine the prosecution's fiber evidence against Williams.

Charles Morton, a scientific evidence expert who works for a California consulting firm, examined fiber evidence at the crime lab several times for the defense team. It is not known whether Morton will be called to testify in Williams' trial on two murder charges.

FBI fiber expert Harold Deadman and Georgia crime lab microanalyst Larry Peterson have testified that fibers recovered from the bodies of 12 young blacks slain between July, 1979, and May, 1981, could have come from 18 different items found in Williams' house and several cars he drove during that time.

Their conclusions were based on comparisons showing that the fibers had similar "microscopic characteristics and optical properties."

Deadman and Peterson said they did not perform melting or burning tests on fibers from the victims' bodies. Such tests would have provided additional comparison data, but would have destroyed evidence that is a keystone of the prosecution's case.

Bresee holds a Ph.D. in clothing and textile sciences and is trying to develop fiber comparison tests using laser light.

If Bresee testifies as a defense witness, he is expected to suggest that the prosecution's fiber experts should have performed more extensive tests before concluding that the fibers show that Williams had contact with his alleged victims.

Williams, 23, is charged with murdering Jimmy Ray Payne, 21, and Nathaniel Cater, 27, who were among 28 young Atlanta blacks whose deaths have been investigated by a special police task force and the FBI.

Meanwhile today, Keith Knox, Williams' life-long friend and former next-door neighbor, testified that he was with Williams during the afternoon and early evening of March 30, 1981, the day a prosecution witness said she saw Williams with Larry Rogers, one of the 28 victims.

Nellie Trammell testified three weeks ago that she saw Rogers, 20, "slumped down" in the front seat of a green station wagon driven by Williams shortly before noon on March 30, the last day Rogers was seen alive.

Knox, 23, said he took a copy of Billboard magazine to Williams' house on March 30. He said he remembers the date because it was the day President Reagan was wounded in an assassination attempt, but conceded later that defense lawyers had reminded him of the date shortly before he testified.

Under cross-examination, Knox also said that shortly after Williams was first questioned by police last May, Knox saw him "removing boxes" from a back room of his house.

Prosecutors have previously suggested that Williams disposed of items containing fiber evidence that could link him to several of the victims.

Knox also described Willie Hunter, a business associate of Williams who testified for the defense, as "effeminate." Knox said Hunter made him nervous.

Several prosecution witnesses have suggested that Williams had homosexual tendencies and expressed contempt for poor blacks.

The defense has responded with witnesses who testified that Williams never exhibited any homosexual behavior and tried to help black children from low-income families succeed in the recording industry.

Mid-way through the ninth day of defense testimony, defense attorney Alvin Binder said the rest of this afternoon's witnesses would be "supportive and cumulative of previous testimony" and therefore asked for an early recess, which was granted.